The present invention relates generally to multi conductor power cables and to separations of the conductors of the power cables.
Typically, a sheath surrounds a plurality of strands in a multi-strand power cable. The sheath is separated together with fillers and any existing bandages of the multi-conductor power cable at a point of break-down. A border zone of the sheath so generated is then covered up with bandages or a fitting piece. Accordingly, a neat cover is provided for the cable, and both water and other undesirable foreign matter are prevented from entering the inside of the cable. Such an arrangement for the separation of strands of a power cable, however, lacks a sufficient mechanical strength necessary to sustain forces which will occur during powerful short-circuit currents.
In power networks subjected to high short-circuit currents, rails or single-conductor cables at wide phase spacing are usually employed. Such conductor systems are not only costly but also require in most instances additional equipment for their installation. Furthermore, such arrangements will often result in an unacceptably high voltage drop. Therefore, (for power networks for the intrinsic needs of nuclear power plants) special cables were developed. These special cables include, in addition to other measures, bandages that are placed under the sheath to improve the resistance of the cables in the event of short circuits.
If the above-discussed measures for separating the strands of a power cable are used in the case of the special cables, a sharp edge is created at the dividing zone of the cable after the bandage or the sheath has been cut. The strand insulations will then be pressed against the edge by the forces activated during the short-circuit current. Such pressure against the edge will likely cause compressive deformations and indentations in the insulation of the strands, resulting in sheath fractures as well as axial shifts between the insulation and the sheath. The insulations are eventually punctured and the effectiveness of the arrangement for the strand separation will be completely destroyed.
It is therefore a particular object of the present invention to provide an arrangement for the strand separation of a multi-conductor power cable which arrangement can be used in networks having extremely high short-circuit currents.
It is another object of the present invention to provide a separation arrangement for a power cable which can absorb the same degree of mechanical forces generated by short-circuit currents at the unseparated cable.
Finally, it is an object of the present invention to provide a separation arrangement for a power cable which can be manufactured by an economical and simple method.
The present invention solves these and other problems in the manner set forth in the following detailed description of the present invention.
In this way, it is advantageous that the resistivity of the strand insulations and of the cable sheath to the effects of the mechanical forces, especially those mechanical forces generated by powerful short-circuit currents, is strengthened. The strengthening occurs as a result of the distribution of the pressure, exerted by the edges, over a relatively large area.
An advantageous application of the present invention, directed at a greater resistance to short-circuit currents, employs simple and commercially available members in the arrangement of the present invention.
A particularly effective protection against leakage current is attained by shrunk-on members of the present invention.
The use of a shrunk on fitting member to enclose the separation structure provides mechanical and chemical protection, for example to prevent any moisture from entering the cable.